Hydraulic control system



Dee. 1 2, 19.44. R L, LEVY 2,365,091

HYDRAULIC CONTROL SYSTEM lFiled Nov. 2s, 1941 Patented Dec. 12, 1944 UNITED STATES PATENT OFFICE ciete dlnvcntions Aeronautiques et Mecaniques S. I. A. M., Fribourg, Switzerland Application November 28, 1941, Serial hlm-420,875 In France September 20, 1940 (Cl. GII- 51) Claims.

Various devices are already known for admitting a liquid into a working circuit, under a. pressure proportional to the force exerted upon a control member, for instance with the object of controlling vehicle brakes.

These devices comprise essentially a hydropneumatic accumulator containing a liquid under high pressure, andan apparatus which may be termed a-liquid operated pressure releasing apparatus and permits a progressive transfer of the pressure reigning inside the accumulator, towards the working circuit, for instance the brake cylinders.

The braking action, as likewise a number of hydraulic actions in other elds, comprisesL two distinct steps, viz.: firstly the movement of the brake blocks towards the brake drum, with a correspo-nding movement of the liquid but no appreciable motive force, and secondly the exertion of the braking force, with a corresponding practically zero displacement of liquid but progressive transmission of energy effecting the braking.

The devices of the said liquid operated pressure releasing type are particularly apt for exerting a progressive pressure in a work piping, but will not give entire satisfaction for rapid filling of such a piping.

Their application in brake mechanisms or any other similar hydraulic applications therefore give rise to two main drawbacks, the first of which is a certain lag in the transmission of theV braking action, and the other an untimed production of water-hammering due to the fact that the pipings are forced to fill with very high pressure liquid.

The object of the present invention is to avoid these drawbacks and the invention consists mainly in using, for effecting the braking or similar actions, two hydro-pneumatic accumulators, one of which, operated under low pressure, ,causes the rapid filling of the brake or other circuits by means of large cross-section pipes and ceases to act as socn as the filling is effected, while the progressively increasing force necessary for tightening the brakes is then set up by the second accumulator, operating under high pressure.

According to another characteristic of the invention, the switching over from one accumulator to the other may be effected by the combination o-f a calibrated valve with a relay arranged on the large cross-section pipe, between the low pressure accumulator and the members to be controlled, said valve remaining closed-and thus setting up the action of the relaywhen the pressure ahead of the valve is less than a predetermined value, while, when the pressure exceeds said value, the valve will open and set up communication between the work circuit and the high pressure accumulator.

The system is controlled by acting upon a distributor connected to the high pressure accumulator, to the tank and to the circuit feeding the valve. The distributor may be of a type known per se.

Another advantageous characteristic of the invention is that a sole, high pressure, pump is used for filling both accumulators. In the low pressure accumulator, the limitation of the pressure to the required value, of the order of for instance lbs. sq. in., is obtained by two distinct means: firstly by a stop limiting the stroke of the piston inside the cylinder of this accumulator when the pressure of the air above said piston has attained the chosen value, and secondly by the presence of a hydraulic pressure release device, which, for the same value of the pressure, disconnects the low pressure accumulator from the pump and causes the latter to discharge into the high pressure accumulator.

A hydraulic control system according to these various characteristics and comprising, besides, a number of auxiliary devices, is shown diagrammatically on the annexed drawing, in which:

Figure 1 shows the entire system applied to the control of vehicle brakes, and

Figures 2 and 3 show respectively, in section, the hydraulic pressure release device and the relay.

The system comprises, for the control of the group of brake cylinders I, 2, two accumulators: a high pressure accumulator 3 and a low pressure accumulator I, a pump 5, a distributor 6 actuated by a pedal l, a lever o1` the like, a tank 8, a large cross-section pipe 9 connecting the low pressure accumulator to the work circuit l0 which, in this instance, supplies the brake cylinders I and 2, a hydraulic relay I2, a calibrated valve I3 mounted in a piping II of a smaller cross-section than piping 9 and coming from distributor 6, a pipe Il. I5 connecting the pump 5 to the accumulators, a pipe I6 connecting the high pressure accumulator to the distributor 6. two pipes I'I and I8 respectively connecting pump 5 and distributor 6 to the tank 8.

The high pressure accumulator 3 is of the known type comprising a piston I9 covering a column of liquid 20.

In the low pressure accumulator 4, the piston u (Figure 2) comprising, inside a liquid-tight' chamber, a piston 25 subjected to the action oi' a spring 26 tending constantly to move a valve 21 away from its seat 28. 'I'his pressure release device communicates with the pump and the accumulator, respectively through the pipe Ii and aperture 29.

The hydraulic relay (Figure 3) comprises, inside a cylinder 3l, a piston 3|, the movement of which in the direction of arrow f causes the backward movement of a double valve 32 movable with respect to a seat 3l and subjected to the action of a spring 3l. The piston 3| itself serves as a seat for said valve and is provided with a channel 35 communicating, through a conduit 36, with the tank l, while two other apertures, provided in the cylinder 30 of said relay, connect the latter on one hand with the low pressure accumulator, through pipe 9, and on the other hand with the work circuit.

Three valves 3l, 38, 39, the function of which will be dened below, are mounted: the first on pipe 9 before the hydraulic relay l2, the second as a by-pass to the calibrated valve I3, and the third on the return pipe 36 to the tank.

The operation of the system is as follows:

Assuming, for xing ideas, that the pressures in the high pressure and the low pressure accumulators are respectively 1400 and 70 lbs/sq. ln., when the operator, for instance the driver, actuates the pedal l of distributor 6, he will set up communication between pipes II and I 6 and at the same time disconnect the distributor from the tank 8. Such distributors, adapted for connecting a control circuit (here pipe II) alternately with a pipe under pressure (Ii) or with an escape pipe (I8), are already known, as particularly from the French Patent 776,289, of October 12, 1933, to the same applicant.

Valve I3 is calibrated in a manner to remain closed as long as the pressure on the accumulator side of it in pipe II, does not exceed say 55 lbs/sq. in.

Under these conditions, during the mst iraction of the distributor operation, the valve will remain closed, so that the pressure will produce, over pipe u and aperture 4| oi' the relay, the motion of piston 3| of the latter. This movement will in turn ilrstly disconnect the relay i'rom the tank and secondly connect pipe a to the work circuit III.

This connection is, moreover, effected suddenly, by the unseating of valve 32 which thereby compresses its spring 24. Pipes 9 and III being of large cross-section, the operation of the relay sets up a rapid iilling of these pipes and, therefore, the immediate application of the brake blocks in cylinders I and 2. Due to the rise of pressure in pipe II under the eiiect of continued action exerted upon the distributor pedal, valve I3 will open, when this pressure on the accumulator side of the valve exceeds 55 lbs/Sq. in.. and set up the tightening oi the brake blocks under a pressure which may be of the order of 130 lbs. for instance.

When the distributor is released, the rapid return of the brake blocks to the nonoperative position is made possible by valve 3l permitting the free ow of the liquid from the brakes to the distributor.

When the pressure in pipe II, at the accumulator side oi' the calibrated valve It, falls below the amount required for actuating relay I2. the spring I4 of said relay becomes operative. thus abolishing the connection between the relay and the low pressure accumulator l, while pipe Il is being connected to tank l through pipe 3l, thus permitting the emptying of pipes I0.

In case the level of relay l2 is insumoient for maintaining the pipes illled with liquid, it will be good to arrange on pipe l0 a check-valve Il adapted to maintain a certain overpressure in the pipes.

The valve 31 has the object oi checking any return oi liquid towards the low pressure accumulator when the pressure provided by distributor t exceeds the calibration value of value I2 The illling of the accumulators is eiTected as follows:

The high pressure pump, l iirst delivers into the low pressure accumulator l. When the latter is charged, i. e., when the stop 23 of piston 2| has struck against the bottom of the cylinder, the pump will deliver into the high pressure accumulator and piston I9 of the latter will rise up to such a level that the pressure of the air above said piston attains for instance 14001bs./sq. in.

This pressure is termed the uncoupling pressure," since the pump I is designed to stop automatically its operation when this pressure is attained, and to start up again automatically when the pressure in the high pressure accumulator has dropped to say 11001bs./sq. in.

The hydraulic pressure release device 24, the object of which is, together with the stop 23, to limit to the required value the pressure inside the lowl pressure accumulator l, further provides operative connection between both accumulators. Thus, if the low pressure accumulator 4 should empty without the high pressure accumulator l having reached the pressure i'or restarting the pump, the hydraulic pressure release device 24 will set up a connection between the accumulators, permitting the low pressure accumulator to ll with liquid drawn from the high pressure accumulator. As this results in a rapid drop of pressure in the latter, the pump will be started up automatically. y

What I claim is:

1. A hydraulic control system, particularly for vehicle brakes or other applications, comprising: a work circuit, a low pressure hydropneumatic accumulator, a rst pipe oi' comparatively large cross-section connecting said accumulator to said work circuit, a tank, a relay interposed in said pipe, a movable member arranged in said relay and the movement of which has the eiect of disconnecting the work circuit from the tank and connecting the low pressure accumulator with the work circuit and conversely, a hydropneumatic high pressure accumulator, a second pipe of comparatively small cross-section connecting the high pressure accumulator and the work circuit, a calibrated valve interposed in the second pipe and opening only when in the latter the pressure on the accumulator side of the valve attains a predetermined value, a third pipe connecting said relay and the second pipe, on the accumula-tor side of the calibrated valve, and permitting lthe pressure reigning in the second pipe to act upon the movable member of the relay, a distributor in said second pipe capable of connecting the calibrated valve alternately with the high pressure accumulator or with the tank, and a checkvalve mounted on the iirst pipe, between the relay and the low pressure accumulator.

2. A hydraulic control system, particularly for vehicle brakes or other applications, comprising: a work circuit, a low pressure hydropneumatic accumulator, a ilrst pipe oi. comparatively large cross-section connecting said accumulator to said work circuit, a tank, a relay interposed in said pipe, a movable member arranged in said relay and the movementof which has the effect of disconnecting the work circuit from the tank and connecting the low pressure accumulator with the work circuit and conversely, a hydropneumatic high pressure accumulator, a second pipe of com-4 paratively small cross-section connecting the high pressure accumulator and the work circuit, a calibrated valve mounted on this second pipe and opening only when in the latter the pressure on the accumulator side of the valve attains a pre-A determined value, a third pipe connecting said relay and the second pipe, on the accumulator side of the calibrated valve, and permitting the pressure reigning in the second pipe to act upon the movable member of the relay, a distributor in said second pipe capable of connecting the calibrated valve alternately with the high pressure accumulator or with the tank, a valve interposed in the second pipe, in parallel with the calibrated valve, and permitting the unidirectional flow of liquid from the work circuit towards the distributor and a check valve mounted on the iirst pipe between the relay and the low pressure accumulator for preventing return of liquid to the low pressure accumulator when the pressure provided exceeds the value of the calibrated valve.

3. A hydraulic control system, particularly for vehicle brakes or other applications, comprising: a work circuit, a low pressure hydropneumatic accumulator, a ilrst pipe of comparatively large cross-section connecting said accumulator to said work circuit, a tank, a relay interposed in said pipe, a movable member arranged in said relay and the movement of which has the eilect of disconnecting the work circuit from the tank and connecting the low pressure accumulator with the work circuit and conversely, a hydropneumatic high pressure accumulator, a second pipe of comparatively small cross-section connecting the high pressure accumulator and the work circuit, a calibrated valve interposed in the second pipe and opening only when in the latter the pressure on the accumula-tor side ofthe valve attains a predetermined value, a third pipe connecting said relay and the second piping, on the accumulator side of the calibrated valve, and permitting the pressure reigning in the second pipe to act upon the movable member of the relay. a distributor in said second pipe capable oi' connecting the calibrated valve alternately with the high pressure accumulator or with the tank, a check-valve arranged between said relay and the tank for maintaining constantly a slight overpressure in the pipes and another check valve mounted on the first pipe between the relay and the low pressure accumulator.

4. A hydraulic control system, particularly for vehicle brakes or other applications, comprising:

a work circuit, a low pressure hydropneumatic accumulator, a first pipe of comparatively large cross-section connecting said accumulator to said work circuit, a tank, a relay interposed in said pipe, a movable member arranged in said relay and the movement of which has the eiect of disconnecting the work circuit from the tank and connecting the low pressure accumulator with the work circuit and conversely, a hydropneumatic high pressure accumulator, a second pipe of comparatively small cross-section connecting the high pressure accumulator and the work circuit, a cali brated valve interposed in the second pipe and opening only when in the latter the pressure on the accumulator side of the valve attains a predetermined value, a third pipe connecting said relay and the second pipe on the accumulator side of the calibrated valve, and permitting the pressure reigning in the second pipe to act upon the movable member Vof the relay, a distributor in said second pipe capable of connecting the calibrated valve alternately with the high pressure accumulator or with the tank, a check-valve interposed on the rst pipe, between the relay and the low pressure accumulator, a valve interposed in the second pipe, in parallel with the calibrated valve, and permitting the unidirectional flow of liquid from the work circuit 'towards the distributor, a check-valve arranged between said relay and the tank for maintaining constantly a slight overpressure in the pipes and another check valve mounted on the ilrst pipe between the relay and the low pressure accumulator to isolate the low pressure accumulator from the circuit when the high pressure accumulator is active.

5. A hydraulic control system, particularly for vehicle brakes or the like, comprising a work circuit, a low pressure hydro-pneumatic accumula*- tor, a first passageway of comparatively large cross-section connecting said accumulator to the work circuit for effecting rapid filling of said circuit, said accumulator ceasing to operate as soon as the filling is completed, a high pressure hydropneumatic accumulator, a second passageway of comparatively small cross-section connecting the high pressure accumulator to the work circuit, a relay interposed in the rst passageway, a loaded valve interposed in the second passageway and adapted to open only when the pressure in the second passageway on the accumulator side of the valve attains a predetermined value, a third passageway connecting the relay to the second passageway at a point between said valve and the high pressure accumulator, a tank, a fourth passageway connecting the relay to the tank, a distributor interposed in the second passageway, a mth passageway connecting the distributor to said tank, said distributor being adapted to control the ow of liquid from the high pressure accumulator ,to said loaded valve or from the second passageway to the tank on the accumula.- tor side of the loaded valve, said relay including movable means responsive to pressure in the second passageway at the accumulator side of the loaded valve for controlling the passage ot liquid through the first passageway to the work circuit or from the work circuit through the fourth passageway to the tank. l

REN LUcmN LnvY. 

